1. Technical Field
This invention relates generally to thermal printers which press dye donor and dye receiver media between a printhead and a platen during printing.
2. Background Art
Referring to FIG. 1, a thermal printer 10, known in the art, includes a resistive thermal printhead having a substrate 12 which carries a printhead 14. A dye donor medium (sheet or web) 16 and dye receiver medium (sheet or web) 18 are passed through the nip formed between the printhead and a platen 20 while heat is selectively applied to the dye donor medium by image-wise energizing the heater elements that make up the thermal printhead. Dye is transferred from the dye donor medium to the dye receiver medium.
Platen 20 typically has an elastomeric surface which yields under pressure. This provides traction for the dye receiver medium, and also insures that the dye donor medium is pressed against the printhead despite any possible contouring which might be present in the printhead surface. FIG. 2 shows the effects of application of pressure by printhead 14 to the media and compliant platen 20. End portions 22 of platen 20 are not under pressure, and thus do not deform, or deform less than portions of the platen that align with printhead 14. This causes a bulge at end portions 22 during printing.
When, as in certain prior art thermal printer systems, dye receiver medium 18 is wider than the length of printhead 14, the dye receiver medium can be pressed into the edge of printhead 14 by the bulge in end portions 22 of platen 20. This causes undesirable print artifacts and scratches in the finished print.